Light diffusing members, such as covers for lighting fixtures, cover the front surface side of the lighting fixtures and diffuse light from light sources over the entire surfaces of the covers so as to uniformly transmit the light and prevent unevenness of brightness on the light-transmitting surfaces. At the same time, the light diffusing members mask the image of the light sources so as to enhance the quality of appearance of the lighting fixtures.
Conventional light diffusing members are manufactured by molding resin sheets containing white pigments. Examples of white inorganic pigments used include silicon oxide, barium sulfate, calcium carbonate, titanium oxide, mica, magnesium oxide, talc, aluminum hydroxide, and aluminum oxide. These pigments can diffuse light but may decrease transmittance of light as the amount of the pigments added increases, which inevitably leads to poor brightness. Furthermore, inorganic particles of these materials may degrade surfaces of the light diffusing members and cause chalking.
There is known a light diffusive coating composition containing an acrylic resin, a fluororesin and organic fine particles that can solve the conventional problems (for example, Patent Literature 1). The composition can provide a high light diffusive layer. However, there remains a need for improvement in transmittance when the composition is used for LED lighting fixtures which have received increased attention. Since the reason for using LED lighting fixtures is to provide energy savings, higher light transmittance is required for cover members for LED lighting fixtures than that required for conventional cover members for fluorescent lights. Furthermore, since LED light sources have high directivity, higher light diffusibility is also required so that the LED light sources are not recognized as point light sources.
In order to achieve both high light diffusibility including a function to mask a light source image and high light transmittance, there is proposed a light diffusing body including a transparent substrate, an internal scattering layer and a surface shaping layer provided on the substrate, the internal scattering layer including particles and a binder (for example, Patent Literature 2). Patent Literature 2 teaches that a refractive index difference between the particles and the binder set to a predetermined value or smaller, and the particles have a mean particle diameter within a predetermined range, so as to exhibit high masking performance and light utilization efficiency.